Nanocomposites are polymer systems containing inorganic particles with at least one dimension in the nanometer range. Some examples of these are disclosed in U.S. Pat. Nos. 6,060,549, 6,103,817, 6,034,164, 5,973,053, 5,936,023, 5,883,173, 5,807,629, 5,665,183, 5,576,373, and 5,576,372. A common type of inorganic particle used in nanocomposites are phyllosilicates, an inorganic substance from the general class of so called “nano-clays” or “clays”. Ideally, intercalation should take place in the nanocomposite, wherein the polymer inserts into the space or gallery between the clay surfaces. Ultimately, it is desirable to have exfoliation, wherein the polymer is fully dispersed with nanometer-size clay platelets. Due to the general enhancement in modulus or stiffniess qualities of various polymer blends when clays are present, there is a desire to have a nanocomposite with high modulus and/or stiffness for automotive or appliance applications that maintains the modulus and/or stiffness after long term heat aging (LTHA).
WO 98/09995 suggests that phenolic compounds can be used as free radical inhibitors during polymerization without deactivation of transition metal catalysts. The subject of this document purportedly includes a process for inhibiting deterioration in a polymer by adding a free radical inhibitor during or before polymerization. Additionally, inhibitor addition during or before polymerization purportedly is advantageous in that it results in good mixing and avoids processing steps such as melting formed polymer. This document does not disclose nanocomposites or use of organo-clays in combination with stabilized polymers.
U.S. Pat. No. 2,982,756 suggests method of stabilizing polymers against oxidative degradation. This document further suggests that oxidative degradation of α-olefin polymers purportedly can be prevented and the polymers stabilized by incorporating in them, in addition to the organic non-staining antioxidant, a minor amount of elemental sulfur.
U.S. Pat. No. 6,451,897 suggests a nanocomposite material comprising a smectite clay having exchangeable cations that is treated with at least one organic swelling agent, uniformly dispersed in a graft copolymer having a backbone of a porous propylene polymer material, to which is graft polymerized at least one grafting monomer capable of being polymerized by free radicals, wherein the total inorganic content of the composite material is about 0.5% to about 10% based on the total weight of the composite.
One method to improve nanocomposite performance is to try functionalized polymers blended with clay. This approach has been limited to materials that are soluble in water or to materials that can be incorporated into the polymerization reaction. This approach has been used to prepare nylon nanocomposites, using for example, oligomeric and monomeric caprolactam as the modifier. Polyolefin nanocomposites, such as polypropylene nanocomposites, have utilized maleic anhydride grafted polypropylenes to form nanocomposites. However, these polypropylene nanocomposites are generally deficient in thermal stability (LTHA) for high physical property demanding nanocomposite applications.
Thus for high stiffness applications such as automotive parts, it would be advantageous to have a nanocomposite that not only improves mechanical properties, but improves thermal stability as well.